It is of importance that the animals maintain an optimal condition for the production of milk, i.e. that their musculature and extended fatness be such so as to retain them in an optimal healthy condition for producing milk. Part of the fat and the muscles is used at the beginning of the period of lactation because of energy deficiency. There is a so-called mobilization of physical reserves. After having calved, a cow normally looses forty to fifty kilograms of her weight, mainly in the form of fat. However, in extreme situations this loss may be much greater. In the course of the period of lactation these reserves are made up again and in particular by the time when the animal is set dry, the animal should have attained a condition that should be maintained until it has calved again. Taking into account the weight pattern shown in the course of time, in particular in the course of the lactation period, it is of importance that the treatment of the animal be such that its physical condition is optimal for producing milk.